An automatic analyzer dispenses samples composed of biological samples, such as blood, urine or the like into reaction containers on a reaction line from sample containers, further dispensing reagents into the reaction containers on the reaction line from reagent containers, measuring mixed solutions of samples and reagents by using a measurement device such as a photometer to execute qualification analysis or quantitative analysis.
A tip of a dispensing probe is immersed into solution to be dispensed at the dispensing operations of sample and reagent, the quantities of the solution attached to the outer wall of the probe becomes large in proportion to the immersion depth of the probe into the solution, so that the quantities of contamination to the probe becomes large.
Accordingly, in order to reduce the immersion depth of the dispensing probe into the solution to the utmost, the motion of the probe is controlled generally as follows. The surface of the solution in the container is detected, the down movement of the probe being stopped when the tip of the probe reaches to the position which is slightly downward from the surface of the solution. Subsequently, a predetermined quantity of the solution is sucked into the probe. A Method for measuring the electrical static capacitance between the dispensing probe and the solution to be dispensed is used as means for detecting the surface of the solution to be dispensed. In this method, the surface of the solution is detected by using the very large change of the electrical static capacitance at the time when the dispensing probe contacts to the solution to be dispensed.
At the dispensing operation using a dispensing probe, a predetermined quantity of liquid may not be dispensed correctly because of a liquid surface detection failure caused by bubbles or the like on the liquid to be dispensed, solid materials in the liquid to be dispensed, or the like. This means that the reliability of an automatic analyzer is damaged largely.
Large numerous automatic analyzers are suggested as means for solving the above deficiency, each of the automatic analyzer including a pressure sensor installed in a dispensing flow passage including a sample probe in order to detect a clogging condition or the like of the sample probe on the basis of the fluctuation of the pressure.
The patent document 1 discloses the technique for detecting an abnormal of suction operation on the basis of the Mahalanobis distance calculated from the reference data made by time series data of pressures at normal sucking operations and the comparison data of time series data of the output values from the pressure sensor at sucking operations.
According to the patent document 1, the reference data are prepared in accordance with the dispensing conditions including the quantity of the liquid to be dispensed, and an abnormal condition can be detected correctly at different dispensing conditions. Further, abnormal conditions are detected by calculating the Mahalanobis distance on the basis of the time series data of pressures of all intervals from the start to the end of the suction operation, so that not only an abnormal condition caused by the specific cause but also abnormal conditions caused by various causes can be detected.